MIA-TPA overnight -LAX-MEL will aa let me check bags thru at MIA
 

Simple question:
I am traveling MIA-TPA with an 18 hour overnighter at TPA, then TPA-LAX (12 hours) then on to MEL (QF) will aa let me check my bags all the way to MEL when I check in at MIA? Are there any pitfalls in doing this?

No. AA will not check for connections greater than 12 hours. It's a computer says no situation. Can't remember if the cutoff is 11:59 or 12:00, so not only will you have to collect at TPA, you may have to collect at LAX (depending on the exact length of your layover).

You can ask at check-in, and they may be willing to find a way to do it, but I would plan as if the answer will be no.

A TA also once explained to me that their computers can't handle a request to check a bag on to a flight that is not the next instance of that flight number. So, for instance, if there's a QF94 LAX-MEL departing in 5 hours and another departing the next day (29 hours), the computer can't understand that you want the one in 29 hours. (I have no independent knowledge as to whether this is true, but this TA seemed quite knowledgeable.)

I've managed to get the computer to do that, so I wouldn't say it's impossible. Just highly inadvisable.

I would suggest looking into a baggage storage service at TPA rather than increasing the odds of your bags being mishandled by leaving them in the system all night.

Thanks for the info. This topic always confuses me. I live in the USA but have done the same thing in the EU. I always get a confused look when I only check my bags part of the way. Just this January FCO-VIE (stop 20 hours)-MIA, the TA at FCO thought it really odd that I wanted my bags in VIE. Had the same happen doing TXL-CPH-LHR(stop 18 hours)-BCN, you want to collect bags in LHR not BCN???

Not that leaving bags in the hands of MIA handlers for any more time than minimally possible is a good idea anyway.